Heaters are used in petrochemical installations to heat fluids for a variety of purposes, typically to break apart larger hydrocarbon molecules into smaller molecules. The heaters contain tubes, up to and even more than a kilometer long in each of several passes, that pass first through a convection section of a heater and then through a radiant section. During use, the heater tubes gradually become contaminated on their insides. This contamination, often called coke, tends to degrade the efficiency of the heater over time and can eventually cause the heater to stop working.
Various methods are known for decoking heaters. In one method, the heater is shut down and steam cleaned with high pressure steam. In another method, described for example in U.S. Pat. No. 5,358,573 issued Oct. 25, 1994, by the same inventor, the heater is shut down and pigs with appendages run through the heater until it is clean. In another method, described in U.S. Pat. No. 5,186,815 issued Feb. 16, 1993, the heater tubes are treated while the heater is in operation by injecting solid particles of very small size into the heater tubes, recovering the solid particles at the outlet and recirculating the solid particles back to the inlet of the heater.
Use of pigs to clean heater tubes is very effective since the pigs have a robust scraping action. Heater operators in South America who have used the inventor's method described in U.S. Pat. No. 5,358,573 have asked the inventor to provide cleaning of the heater tubes by pigs while the heater is in operation. The inventor has thus come up with a novel solution to the problem of providing a heater cleaning operation by using pigs while a heater is in operation.